Conventionally, in an image scanner which requires a large image sensor for reading a relatively large object, such as a desktop type, plural chips of the same standard are arranged adjacently, and an image of the object is read by employing output signals from the respective chips. The image scanner having such a structure initially measures gamma characteristics for each chip and compensates each gamma compensation value for each corresponding chip when an image is inputted, thereby resolving manufacture variations among the respective chips so as to obtain a fine image.
However, when chip characteristics are varied due to changes over time or the like, it is necessary to measure and compensate the gamma characteristics on all such occasions. In addition, when there are different gamma characteristics within one chip, the effect appears in an image as the stepwise difference in density on the chip boundary, and such a case cannot be handled by this structure. Further, it is necessary to provide a number of memories on the scanner side to store gamma compensation values for the plural chips.
The conventional image input apparatus is constructed in this manner, and labor that is involved in the maintenance of the plural sensor chips for the compensation of gamma characteristics due to the secular change and the number of memories for storing gamma compensation values are necessary. Further, when there are different gamma characteristics within one chip, this cannot be handled, and as a result, a fine image cannot be obtained.
The present invention is made to solve the above-described problems. Accordingly, an object of the present invention is to provide an image input apparatus which does not require maintenance such as a gamma characteristics compensation of a sensor chip due to the secular change and which can perform the compensation of gamma characteristics within one chip.